Antenna system for satellites

ABSTRACT

In a set of n antennas arranged along a circle, say on a satellite, only m antennas, say those facing Earth are operative at a time and are switched in as they pass into the operative area. The radiating lobes are constrained to be directed permanently towards a substantially unvarying area and the phaseshifting required is obtained by means of digital phase-shifters which operate stepwise, so as to make up for variations of the length of the path between an antenna as it revolves and Earth.

United States Patent Dorier et al.

ANTENNA SYSTEM FOR SATELLITES Inventors: Bernard Louis Marcel Dorier, La Celle Saint-Cloud; Denis Jacques Laedlein, Villennes-Sur-Seine, both of France Assignee: Soclete Nationale DEtude et de Construction de Moteurs DAviation, Paris, France Filed: Oct. 14, 1969 Appl. No.: 866,342

Foreign Application Priority Date Oct. 15, 1968 France ..681700l6 US. Cl. ..343/100 SA, 343/100 ST, 343/854,

- 343/876 Int. Cl. ..H0lq 3/26 Field of Search ..343/100 ST, 100 SA [451 July 25, 1972 [56] References Cited UNITED STATES PATENTS 3,531,803 9/1970 Rosen et al. ..343/100 SA 3,403,401 9/1968 Cragon et al ..343/l00 SA Primary Examiner-Benjamin A. Borchelt Assistant Examiner-Richard E. Berger Attorney-Watson, Cole, Grindle & Watson [5 7] ABSTRACT In a set of n antennas arranged along a circle, say on a satellite, only m antennas, say those facing Earth are operative at a time and are switched in as they pass into the operative area. The radiating lobes are constrained to be directed permanently towards a substantially unvarying area and the phase-shifting required is obtained by means of digital phase-shifters which operate stepwise, so as to make up for variations of the length of the path between an antenna as it revolves and Earth.

7 Claims, 5 Drawing Figures PATENTEDJULZS m2 3.680.113 SHEET 2 OF 2 Phase shift (ms) li phase shifter time switch/by gfl phase shifter time 6 l j sw/tch/ng 3 2 fi /785E 5mm I 4 M phase shifter s w/t ch/ng 1 tlhve Jlmwzg/ ANTENNA SYSTEM FOR SATELLITES Our copending application Ser. No. 649,550 filed June 28, 1967, now abandoned, discloses a method for feeding an aerial system including n elementary sources distributed along a circle or the like closed line, said method consisting in feeding simultaneously only a group of limited number m of successive elementary sources and in executing in said group of transiently fed supplies a stepwise periodical shifting by cutting out at each step that fed source which lies at one end of said group while a further elementary source is incorporated with the group at its other end.

Said method is of a particularly interesting application in the case of an antenna system carried by an artificial satellite of Earth which has been stabilized on its orbit by a spin or rotary movement at a comparatively low speed, since it allows the antenna to radiate in a particular direction which is defined in a manner such that the main lobe of the antenna radiation covers all or at least part of the visible surface of Earth as seen from the satellite. In other terms, said main lobe should be constantly directed towards the center of a predetermined area of Earth in spite of the rotation of the satellite which carries the antenna system.

Our above-referred to prior application discloses also a circuit feeding such an antenna system and which requires only electronic control means while cutting out all moving mechanical parts. Such a circuit resorts chiefly to a set of m phase shifters, for instance of the ferrite type, In being defined as being the limited number of elementary sources fed simultaneously at any predetermined moment, said phase shifters being in their turn associated with a set of km switches preferably constituted by ferrite circulators, k being an integer.

In order to compensate permanently and accurately the phase shifting produced by the rotation of the satellite and corresponding to a sinusoidal modification of the projection of the elementary generator considered over the geo-central line of the satellite, that is the line joining the latter to the center of Earth, the use of continuous or analogic phase shifters has been proposed by us so as to make up for this slight modification in the distance between the generator and Earth as said generator moves towards and away from the latter as it revolves with or on the satellite.

However such a perfect accuracy and continuity in the execution of the phase shifting are by no means compulsory and on the other hand, they are the cause of various objectionable restraints which are not justified by the counterpart of a better accuracy and continuity.

Our invention has now for its object a modification of the means feeding an antenna system, said modification providing in particular a reduced control power and an increased reliability while its radio-electric performances are retained; this is obtained by resorting to digital phase-shifters that is phase shifters operating through discrete or discontinuous steps. Such digital phase shifters are well-known for anyone skilled in the art and it is therefore unnecessary to give a detailed description thereof. By way of example reference may be made to the US. Pat; to Anderson No. 3 039 94.

Our invention covers the incorporation of digital phase shifters with the antenna system forming the object of our prior application and it covers also a practical embodiment thereof ensuring an optimum operation with a view to reaching the objects mentioned hereinabove.

Said optimum operation requires the best association of good radiation properties and reduced control power as provided by resorting to a law governing the phase and defined digitally by means of a minimum number of discrete modifications in phase for a predetermined rate of modulation, that is a modification of the electromagnetic field received in a predetermined direction during the rotation of the satellite.

Further features and advantages of the invention will emerge from the description of a preferred embodiment of the invention, given by way of example only, with reference to the accompanying drawings.

In the drawings:

FIGS. 1 and 2 illustrate schematically how the elementary antennas are distributed;

FIG. 3 is a diagram of the feed circuit to the elementary antennas;

FIG. 4 illustrates the operation of the phase shifters according to the invention; and

FIG. 5 is a perspective view of the satellite equipped with antennas in accordance with the invention.

FIGS. 1 and 2 show 12 elementary antennas disposed around a cylindrical surface. In order to ensure that there is a directional property in the plane of transmission, each elementary antenna comprises three elementary sources disposed in line, these sources being flat spirals in order to produce circular polarization. The antenna A thus takes the form of a cylinder which carries a network of flat spirals (see FIG. 2), each group of three flat spirals, arranged in line on a generatrix, constituting one of the twelve elementary antennas or elements of the network. The axis of the cylinder is parallel to the axis of rotation X-Y of the assembly of the satellite (see FIG. 5) where S is the body of the satellite equipped with solar cells C. On an axial mast there are situated a control antenna T, a receiving antenna Ar and a transmitting antenna Ae, the latter two antenna being associated with respective feed circuits located at R and E.

The 12 elements of the network are arranged in the manner above described and are fed in the manner illustrated in FIG. 3, the feed circuit comprising three continuous phase-shift elements D1, D2, D3, and nine switches C1, C2 C9.

The joint use of the switching system in question and of ferrite-based circulators to create the switches has the advantage that switching is efi'ected progressively without disturbing the feed phase, the circulators being field-shift devices. More generally, any desired switch could be used for the purpose of switching.

The continuous phase-shift devices are designed to permanently cancel out the phase-shift due to rotation of the satellite, in order to maintain the direction in which radiation from the different sources is in phase.

According to our present invention, the program of the modification of the bit or discontinuous change of condition of the various digital phase-shifters is such that modifications affecting simultaneously any two phase-shifters are cut out systematically. In other words, the control of the phase shifting is designed so as to satisfy the criterion of modifying one bit on a single phase shifter at a time, this being obtained in order to reduce the total amplitude of disturbances in the radiated field.

in the stepped diagrams showing the discrete values or bits in the phase shifting of the various digital phase-shifters as functions of time, the steep vertical edges of the different diagrams are never in registry and it is necessary to act on the duration of the level sections in order to ensure the nonsynchronization which is a feature of our invention.

According to a technical feature of our invention, the phase corrections are executed at separate moments during equal times in order to simplifythe controlling program.

In order to further simply the procedure, the phase shiftings may advantageously all produce the same discrete phase-shifting values, that is in the case of stepped diagrams the steep vertical edges are all of a uniform height. According to a still further technical feature of our invention care is taken during the sequential phase shiftings to provide a progression which always assumes the same direction without any reverse movement. To this end, the lowest possible correction is obtained by acting only on the bit showing the lowest weight in a phase shifter. Furthermore the selection of a quantified law varying gradually in accordance with the modifications of the theoretical law requires a minimum number of changes in condition of the phase shifter. The change in condition of the bit having the lowest weight in a phase shifter leads moreover to a correction of a corresponding magnitude in the angular setting of the radiating lobe of the antenna whatever may be the phase shifter concerned. This allows the angular corrections to be executed at a uniform rhythm.

The single figure of the accompanying drawings shows the above-mentioned operative diagrams of the digital phase shifters according to our invention, the number of said phase shifters being equal to four in the example illustrated.

To understand said diagram reference may be made to the description of the drawings accompanying our above-mentioned prior application. The only exception relates to graphs D1, D2 and D3 on FIG. 5 of the latter. It is therefore unnecessary to repeat said disclosure.

In a manner similar to that disclosed in our prior application and resorting to the same notations it should be remembered that at any moment m out of the n generators with which the elementary sources of the cylindrically shaped system are alined are fed through the agency of an equal number m of phase shifters.

Resorting as proposed by our present invention to digital phase shifters providing p bits which allow 2 possible values to be displayed for the insertion phase this leads to an uncertainty as to the phase of each of the fed generators by i 11 max/ 2" l where r1: is the maximum phase shifting to be taken up.

In order to obtain an optimum incorporation of digital phase shifters and to approximate the theoretical phase by the quantified phase shiftings, a law which satisfies the abovementioned criteria is illustrated by the operative diagrams of the phase shifters on the accompanying drawing for a predetermined law of phases corresponding to the case of a system including n l6 generators fed by digital phase shifters providing p 3 bits and consequently 2 8 discrete values. Said criteria are as follows:

modification of a bit on one phase shifter at a time in order to reduce the total amplitude of the disturbances;

phase corrections executed at moments separated by equal time intervals in order to simplify the controlling program.

lf furthermore it is admitted that the phase shifter is not corrected at the moment of the actual shifting of the sources, the total number of possible phase corrections is Consequently if T is the period of rotation of the satellite, a duration is selected for the spacing in time between two successive phase corrections. A clock controlled by the rotation of the satellite supplies periodical pulses which are sent into a counter which is zeroized after each revolution of the satellite, said counter including p binary flip flops (2 2 I T) A decoding matrix provides then means for selecting the suitable combinations out of the products of the p binary variables in order to satisfy the previously established phase governing law the matrix executes for this purpose logical products of the outputs of the binary flip-flops. The signal obtained when the result registers with the combination controlling the change-over of one phase shifting bit is then sent into the corresponding phase shifter through the agency of the control means.

The law governing the phases is then ascertained by finding for each of the precedingly defined intervals which combination between the elementary phases ensures a satisfactory deflection of the radiating lobe, care being taken to provide a modification in phase only for a single phase shifter when one passes from one time interval to the next.

Thus each of the elementary signals is controlled in accordance with a theoretical phase-governing law which is approached in a quantified manner through the digital phase shifters. The phase orders being displayed, the radiation lobe revolves in synchronism with the antenna until an angular correction appears on one phase shifter and reset; the direction of maximum radiation. The digitalized phase-governing laws of two successive phase shifters are defined with reference to tune by a delay corresponding to a rotation by 211/" of the satellite.

We claim:

1. A rotary antenna system radiating toward a stationary area comprising a set of n elementary sources distributed along a closed line substantially perpendicular to said area and of which a group of a reduced number m is selectively operative at any same time, means selectively feeding said group of m elementary sources to operate them exclusively of the other sources, means applying a stepwise switching of the sources to cut out the source at one end of the group considered in a predetermined direction and to incorporate with the group at the other end thereof the next elementary source with a view to producing a stepwise progression, within the set, of the group of elementary sources fed by said feeding means, digital phase-shifters operating with discrete phase-shifting values compensating the modifications in the distance between the rotary operative sources and the stationary area, and means for cutting out systematically the modifications affecting simultaneously any two digital phase-shifters during the progremion of a bit modifying program constituted by a stepwise change in condition of the various phase-shifters.

2. An antenna system as claimed in claim 1 wherein the information data defining the phase shifting to be controlled are stocked in a memory constituted by a decoding matrix associated with a controlled clock.

3. An arrangement as claimed in claim 1 wherein synchronization in operation of successive phase-shifters is cut out by acting on the duration of maintenance of each of their conditions before their change of condition.

4. An arrangement as claimed in claim 1 wherein the phase shiftings are executed at different moments separated by equal time intervals.

5. An arrangement as claimed in claim 1 wherein all the phase-shifters operate with the same discrete phase shifting values.

6. An arrangement as claimed in claim 1 wherein the progression of the phase shiftings is always performed in the same direction during the succession of phase shifting operations without any reverse shifting.

7. An arrangement as claimed in claim 1 wherein phase shifting is obtained by phase shifting modifications equal to the modifications of the bit of the lowest weight in a phaseshifter. 

1. A rotary antenna system radiating toward a stationary area comprising a set of n elementary sources distributed along a closed line substantially perpendicular to said area and of which a group of a reduced number m is selectively operative at any same time, means selectively feeding said group of m elementary sources to operate them exclusively of the other sources, means applying a stepwise switching of the sources to cut out the source at one end of the group considered in a predetermined direction and to incorporate with the group at the other end thereof the next elementary source with a view to producing a stepwise progression, within the set, of the group of elementary sources fed by said feeding means, digital phase-shifters operating with discrete phase-shifting values compensating the modifications in the distance between the rotary operative sources and the stationary area, and means for cutting out systematically the modifications affecting simultaneously any two digital phase-shifters during the progression of a bit modifying program constituted by a stepwise change in condition of the various phase-shifters.
 2. An antenna system as claimed in claim 1 wherein the information data defining the phase shifting to be controlled are stocked in a memory constituted by a decoding matrix associated with a controlled clock.
 3. An arrangement as claimed in claim 1 wherein synchronization in operation of successive phase-shifters is cut out by acting on the duration of maintenance of each of their conditions before their change of condition.
 4. An arrangement as claimed in claim 1 wherein the phase shiftings are executed at different moments separated by equal time intervals.
 5. An arrangement as claimed in claim 1 wherein all the phase-shifters operate with the same discrete phase shifting values.
 6. An arrangement as claimed in claim 1 wherein the progression of the phase shiftings is always performed in the same direction during the succession of phase shifting operations without any reverse shifting.
 7. An arrangement as claimed in claim 1 wherein phase shifting is obtained by phase shifting modifications equal to the modifications of the bit of the lowest weight in A phase-shifter. 